EF Core中比较Owned类型属性相等时出错的解决方法

实体模型代码 #

public sealed class Author
{
    public int AuthorId { get; set; }

    public Guid AuthorGuid { get; set; }
    public required AuthorName Name { get; set; }

    public ICollection<Book> Books { get; set; } = [];
}

[Owned]
public sealed class AuthorName
{
    [MaxLength(248)] 
    public required string FirstName { get; set; }

    [MaxLength(248)] 
    public string? NickName { get; set; }

    [MaxLength(248)] 
    public required string LastName { get; set; }
}

出错的查询代码 #

.SingleOrDefaultAsync(a => a.Name == author.Name)

错误信息 #

No backing field could be found for property 'AuthorName.AuthorId' and the property does not have a getter

解决方案 #

方案1：重写Owned类型的相等性逻辑 #

EF Core无法自动处理复杂类型的相等比较，直接用==会导致EF误判需要主键字段。给AuthorName实现IEquatable<AuthorName>并重写相等方法，让EF能正确解析比较逻辑：

[Owned]
public sealed class AuthorName : IEquatable<AuthorName>
{
    [MaxLength(248)] 
    public required string FirstName { get; set; }

    [MaxLength(248)] 
    public string? NickName { get; set; }

    [MaxLength(248)] 
    public required string LastName { get; set; }

    public bool Equals(AuthorName? other)
    {
        if (other is null) return false;
        return FirstName == other.FirstName 
               && NickName == other.NickName 
               && LastName == other.LastName;
    }

    public override bool Equals(object? obj)
    {
        return Equals(obj as AuthorName);
    }

    public override int GetHashCode()
    {
        return HashCode.Combine(FirstName, NickName, LastName);
    }

    public static bool operator ==(AuthorName? left, AuthorName? right)
    {
        return EqualityComparer<AuthorName>.Default.Equals(left, right);
    }

    public static bool operator !=(AuthorName? left, AuthorName? right)
    {
        return !(left == right);
    }
}

方案2：查询中显式比较每个属性 #

如果不想修改AuthorName类，可以在LINQ查询里直接比较Owned类型的各个属性，避免EF的自动解析错误：

.SingleOrDefaultAsync(a => 
    a.Name.FirstName == author.Name.FirstName 
    && a.Name.NickName == author.Name.NickName 
    && a.Name.LastName == author.Name.LastName)

方案3：检查DbContext配置 #

确保在OnModelCreating中没有误给AuthorName配置主键，Owned类型不需要独立主键：

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    modelBuilder.Entity<Author>().OwnsOne(a => a.Name);
    // 不要添加类似 modelBuilder.Entity<AuthorName>().HasKey(x => x.AuthorId); 的配置
}

内容的提问来源于stack exchange，提问作者MoRe